[Measurement of linear exposure nominal pose used in curietherapy]

The idea, and subsequent construction, of a dose rate meter for measuring linear exposure dose originated in those pilot centres of Curietherapie which wished to replace radium by the artificial radionucleides, Irdium-192, Caesium-137 etc. The aparatus makes it possible to measure, directly and quickly, the activity of a specified length of a linear source, a measurement which has only been possible until now by dividing the exposure dose by the length whose activity it is desired to know. If the dose-rate obtained by these two methods agrees, this apparatus shortens the time for which the sources need to be handled, thereby reducing the danger of irradiation to staff and technicians. The apparatus is thus able to reveal heterogeneity of activity along the length of a line-source. In the specific case of Iridium, our experience shows that wires which have been used in several applications may develop mechanical bends and constrictions, which can lead to fluctuation in dose rate along their length. The apparatus was first constructed in 1967, after preliminary experiments in 1965. As Curietherapy has become more widely used, the apparatus has undergone many modifications which is more precise and specific than it was initially. At the present time it can only be used with Iridium as wire, and with Caesium in the form of trains of seeds (corresponding to the AGS sources) or needles. Nevertheless, a third scale is under consideration, for use with newer radioelements, which may be used in future.